Incandescent electric material.



No. 770,991- PATENTED SEPT. 27, 1904.

A. VOELKER. INGANDESOENT ELECTRIC MATERIAL.

APPLICATION FILED JUl IE 2,1904.

N O M O D E L.

wait l 'z/enzzr UNITED STATES Patented September 2'7, 1904.

PATENT OFFICE.

AUGUST VOELKER, oE BERLI GERMANY, Ass1GNoE To sooIETE ANO- NYME INDUsTEIE VERRIERE ET sEs DEETVEs A BRUXELLES.

INCANDESCENT ELECTRIC MATERIAL.

SPECIFICATION forming part of Letters Patent No. 770,991, dated September 27, 1904.

Application filed June 2, 1904. Serial No. 210,905. (No specimens.)

To all whom 712% may concern.-

Be it known that 1, AUGUST VonLxnR, electrochemist, a subject of the King of Prussia, Emperor of Germany, residing at No. 56 Unter 5 den Linden, Berlin, Germany, have invented certain new and useful Improvements in Incandescent Electric Material, of which the following is a specification.

Prior methods of heating by means of the electric current may be divided into two classes first, the resistance system; second, the voltaic are system. According to the firstmentioned system use is made of the property of the electric current of heating a conducting-body which offers a very high resistance to its passage. According to the second system, on the other hand, use is made of the prop erty of the current of permanently flowing, although the actual circuit is broken, and of forming a small, highly-luminous flame, the so-called electric are. As typical example of the first-mentioned system of heating, the incandescent lamp may be instanced, while the arc-lamp is an example of the second system. As is well known, however, these systems of electric heating have as yet found but limited application in practice.

The voltaic-arc system produces a very high degree of heat, (about 3,000 centigrade;) but the latter cannot be regulated. Moreover, the electric arc is not chemically pure, owing to the large number of particles of the conductor which are carried over in it, so that the are cannot be employed in melting sensitive material, such as enamel or glass mixtures and the like. Furthermore,the province heated by the arc is very limited, so that it can only be used for heating quite small quantities of material, but not for highly heating melting-chambers 4 even of only limited size. For the latter purpose a combination of arcs is necessary. This system, therefore, as practice has proved is both expensive and impractical.

As regards the resistance methodthat is to say, electrically heating a conductor-there has hitherto been no really Satisfactory conductor for the purpose. For practical purposes the only conductors which have been capable of employment are metal wires, es-

peciallyniekel and platinum, which are wound round the body to be heated or are inserted into such body. In employing such wires the first difficulty is that the wire can only be heated up to the fusing-point of the material of which the conductor is made. Variations in the current strength, defective insulation, irregularity in the section of the conductor may cause short-circuiting, disturbance of the conductor, and thus destruction of the entire and usually very expensive apparatus. Furthermore,such conductors-for instance,plati num wire---on account of the small surface they present are only able to conduct very small amounts of heat, so that on this system only small heating and melting apparatus can be worked, and while the expenses are considerable there is much trouble involved. Small melting-furrmces, such as are employed in laboratories by chemists, by physicians, dentists, and others,and likewise heaters for tramways, &c., constructed on this system, are to some extent in use, but have not yet received general approbation. Electric heating, in fact, has hitherto been a luxury, or where the method has been adopted for industrial purposes it has been in cases where such high temperatures have to be attained as could hitherto only be reached by means of the electric arc.

The problem of heating by means of the electric current cannot be considered as solved-that is to say, electric heating cannot be regarded as within the domain of practical engineeringuntil by some simple, convenient, and safe method large surfaces of any desired extent can be heated by the current in similar manner as by ordinary fuel, such as wood, coal, coke, &c. Furthermore, the temperatures which can be reached must not be too limited and must be capable of exact regulation, while the expenses of working must be moderate. Attempts have been made to solve this task by employing as conductors or heating resistances rods or blocks of carbon or even powdered carbon. Experiments have also been conducted with pulverized carbon mixed with graphite or silicates. These experiments, however, have not proved successful from the practical standpoint. The

reason is that the fact has not been recognized that a carbon conductor, or, better, conducting material consisting of a mass of dis-' be attained if the size of the discontinuousconductor is adapted to the current employed and the proportions of the mixture likewise calculated accordingly.

It has been found that with tensions of two hundred or more volts the employment of grains of from three to seven millimeters in diameter is most suitable,while for a smaller tension grains of from one to three millimeters give the most favorable conditions for conversion of the current into heatthat is to say, for thorough utilization of the electrical energy. Such division of the carbon, however, into grains of a certain size is alone insufficientto render the resistance of the mass perfectly suitable for all possible tensions and strengths of current. Solely by division of the carbon it is not possible (since, for obvious reasons, division into the finest graduations is an impossibility) to produce any desired number of different finely-distinguished masses which in respect to conductivity and power of converting heat only exhibit small differences, so that any desired electric current can be converted into heat under the most favorable conditions. By division alone of the carbon only a limited number of standard, or, rather, main resistance massesthat is to say, groups -can be produced which are suitable, even although only approximately, for a number of currents,the strength and tension of which only vary within certain limits. By treating these main groups again any desired number of the above-referred-to finelydistinguished masses or species may be obtained. Such further treatment of each main group is effected by means of graphite, on the one hand, and of silicates, on the other. By mixing graphite with the carbon the material is rendered more capable of converting the current into heat and of storing up such heat and likewise of conducting the current. Silicates, on the other hand, have the reverse effect. Suppose, for instance, it is desired to produce a resistance material for currents of two hundred volts and more, for which current strengths, as already stated, only grains of from three to seven millimeters diameter can be employed. By division of the carbon material five main groups would be formed:

Group A 3 millimeters, (for 200 to 300 volts.) Group B 4 millimeters, (for 300 to 400 volts.)

Group C 5 millimeters, (for 400 to 500 volts.) Group D 6 millimeters, (for 500 to 600 volts.)

Group E 7 millimeters, (for 600 to 700 volts.)

By the addition of graphite, on the one hand, and silicates, on the other, each of these main groups A to E can be divided, so that, for in stance, the group A is split up into ninety nine species, each successive one being suited for a current one volt stronger than the preceding, thus:

A 3 millimeters for 200 volts.

A1 3 millimeters for 201 volts.

A2 3 millimeters for 202 volts.

AUDI?) millimeters for 299 volts.

B 4 millimeters for 300 volts.

Br millimeters for 301 volts.

Bz l millimeters for 302 volts.

B n millimeters for 399 volts,

fuel is spread over the surface (of Whatever extent) to be heated and exercises its heating efiect partly by resistance and partly by voltaic arc that is, by combination of the two well-known methods raising the temperature to the extent desired from 2,000 to 3,000 centigrade.

The new material, as already indicated, has the form of a more or less finely-granulated mass or powder, which, depending upon the temperature required, is heaped up to a greater or less height around the object to be heated, such as crucible, muflle, furnace-chamber, or the like.

On passing a current of the requisite strength through such layer of material, as above described, an infinite number of very small luminous arcs will be formed between the individual grains, which in a few minutes give to the entire material the appearance of a layer of coke or coal in highly incandescent condition. At the same time the capability is imparted to the material of heating the object it surrounds in the course of a few minutes to the highest temperaturesthat is to say, up to 3,000 centigrade, (the temperature of the electric are.) It will be found,

however, that the material is not, either by combustion or otherwise, consumed to any appreciable extent, but can be employed for months without any change. Short-circuiting and consequent destruction of the object (crucible or melting apparatus) surrounded by the material are, moreover, impossible, nor are any products of combustion formed in the heated space or chamber.

\Vith the new material, moreover, the lowest and most exactly regulable temperatures also can be attained,-when it is desired, for instance, not to concentrate the heat on a melting-chamber, but to allow it to radiateas, for example, is the case with heating apparatus for dwelling-houses and the like. In such case the material, suitably prepared, is not piled up in a layer around the object to be heated, but is placed inside the latter, and a so weak electric current is sent through that the arcs which form between the individual particles of the material are scarcely visible, if at all. The material will then radiate a steady gentle heat. All apparatus which at present are heated with the aid of platinum, nickel, &c., conductors at great expense and at the same time with uncertain results can without exception be heated by the new material. It is only necessary for this purpose to feed the material into the object to be heated in the same manner as ordinary fuel. Still better and, in fact, the best results are to be obtained if one or more of the species of material are employed in the following manner, reference being had to the accompanying drawing, in which the figure shows a vertical section of an apparatus in which a crucible is being heated.

Assume it is desired to melt, say, nickel contained in a crucible a with the greatest economy of current. The chief conditions for economy are that as far as possible only the surfaces in immediate contact with the material to be melted-that is to say, in the present case only the walls of the crucible a be heated, all heat conducted into the interior of the crucible, and all less of heat through heating of parts remote from the surface of the crucible, such as, especially, the walls 6 of the furnace, avoided. Furthermore, the heat must be conducted to the crucible a in particular manner, for in the zone 0 c, as is well known, a crucible requires more heat than in a zone (Z (Z, while in zone 6 e the least heat is necessary. \Vhen the heat, therefore, is conducted to the crucible in uniform manner all over, as has hitherto been the practice, it is found that such crucibles near the mouth-that is, in the upper regionare difficult to heat, so that the contents at this part are not adequately heated, while the bottom of the crucible is burned. These defects can be readily overcome by means of the resistance material manufactured according to the present process.

As already explained, with the aid of my new process suitable resistance material can be prepared for currents of all strengths and tensions. If now we suppose that the layer N is that which offers least resistance to the flow of current through the wires f g, while the layer M is of material so compounded that it does not allow the current to pass at all or only a verylimited portion of it, it is obvious that the current conducted to the positive (l) terminals will pass solely through the material N- that is to say, along and as close as possible to the surface of the crucible a to the negative poles. It is therefore practically only in the material N that the minute luminous arcs will be formed, and only this layer will be intensely heated and will transmit its heat to the crucible. The layer M, on the contrary, will only be slightly, if at all, traversed by what may be called ,stray waves of current, and therefore will be heated but slightly, if at all, and thus will only act as an exceptionally good insulator of heat. Exhaustive experiments have shown that apparatus designed on the above principles and fed with material of the kind described radiate practically no heat, while in the interior the highest temperatures are reached.

As will be readily understood, by means of suitable and complicated combinations of materials compounded according to the new process any degree of heat, even of the subtlest and most complicated nature, can be generated in a heating apparatus, depending upon the variety of the species on materials and the manner in which they are heaped up that is to say, whether more or less closely packed and whether in thick or thin layers, &c.

Having thus described my invention, what I claim as new, and desire to secure by Letters Patent, is*

The process of manufacturing an incandescent electric material, consisting in granulating carbon until the grains are from substantially one to seven millimeters in size, next dividing the material so obtained into groups, the first group of which contains only grains of one millimeter in size, the second only two millimeters, and so on, and then graduating each of the said groups by theaddition of graphite or of silicates, depending upon whether the conductivity of the group is to be increased or decreased, substantially as described.

In witness whereof I have hereunto signed name, this 14th day of May, 190a, in the presence of two subscribing witnesses.

AUGUST VOELKER.

lVitnesses:

HENRY HAsPun, VVOLDEMAR HAUPT. 

